Droplet transport device, analysis system, and analysis method

ABSTRACT

Provided is a technique for moving all of a droplet from a microchannel in which the droplet have been introduced to another layer.The droplet transport device of the present disclosure includes a substrate having a through-hole or a recess, a first electrode provided on the substrate along the surface of the substrate and arranged at a position adjacent to the through-hole or the recess, a plurality of second electrodes provided on the substrate along a surface of the substrate and to which a voltage for moving the droplet introduced on the substrate is applied, and a dielectric layer covering the surface of the substrate, the first electrode, and the second electrodes, and a water-repellent film provided on the inner wall surface of the through-hole or the recess, and on the dielectric layer.

TECHNICAL FIELD

The present disclosure relates to a droplet transport device, ananalysis system, and an analysis method.

BACKGROUND ART

In the analysis of liquid samples such as bioanalysis, it is required toperform the desired analysis using as little sample or reagent aspossible. This is not only to reduce the burden of sample collection bykeeping the sample collected from the analysis target such as a livingbody as small as possible but also to use a sample that exists only in asmall amount from the beginning, such as criminal evidence, for analysiswithout waste.

For example, Electro Wetting On Dielectric (EWOD) is attractingattention as a technique for manipulating (transporting, mixing, and thelike) a very small amount of liquid of 1 microliter or less on asubstrate. In EWOD, a device in which transport control electrodes arearranged on a substrate and a water-repellent treated dielectric iscoated on the transport control electrodes is used. Droplets can becontrolled by utilizing the phenomenon in which the contact angle of thedroplets on the dielectric surface changes by introducing minutedroplets onto such a droplet transport device and applying a voltage tothe transport control electrode to change the surface energy of thedielectric. Using a droplet transport device makes basic operationspossible, for example, such as attracting droplets to a position of anelectrode to which a voltage has been applied to transport the droplets,transporting two droplets onto one electrode to mix the droplets,repeatedly moving the mixed droplets by some pathway to stir the mixeddroplets, or the like.

In general, the pathway through which the droplets are manipulated oftenhas a form in which an upper substrate covers the pathway from above alower substrate having the transport control electrode in order toprevent evaporation of the droplet (a form in which the dropletmanipulation pathway is sandwiched between the lower substrate and theupper substrate: hereinafter referred to as “microchannel”). In such amicrochannel module (droplet transport device), it is useful if anoperation, for example, such as that a certain amount of the liquidinjected from an opening (hole) provided in the upper substrate isintroduced into the microchannel, is possible in addition to the abovebasic operations, and a method for introducing a droplet into a desiredmicrochannel through a hole is being studied (PTLs 1 and 2 and Non-PTL1).

In PTL 1, in order to introduce droplets from the outside into themicrochannel, disclosed is a configuration in which a hole is made in anupper substrate of the upper substrate and a lower substrate, a liquidis supplied from above the hole, and a part of the liquid can be tornoff and introduced into the microchannel as minute droplets. By makingthe inner wall surface of the hole a hydrophilic surface, some of thedroplets larger than the hole can enter the inside of the hole, and theportion that has entered the hole can be torn off by the operation ofthe electrode and introduced into the channel. In the configuration ofPTL 1, it is disclosed that, if the inside of the hole is madewater-repellent, droplets larger than the hole cannot enter the hole andcannot be torn off, so that the inside of the hole needs to behydrophilic.

PTL 2 discloses the configuration in which, a hole is made in an uppersubstrate of the upper substrate and a lower substrate that sandwich amicrochannel, and a part of a relatively large amount of liquid in amicrochannel cell can be discharged as minute droplets (see paragraph0040 and FIG. 8 of this document). PTL 2 discloses the principle: boththe inner wall surface of the microchannel and the inner wall surface ofthe hole remain water-repellent; at the time when the liquid in themicrochannel is transported to the position of the hole by the transportcontrol electrode if the surface where the droplets are in contact withis water repellent, the curvature of the droplets will increase; thegreater the curvature, the higher the pressure inside the liquid, andthus, some of the liquid in the channel can be pushed upward(discharged) from the hole.

Both PTLs 1 and 2 aim to cut out a part of the original liquid as minutedroplets. PTLs 1 and 2 have a difference; in PTL 1, a part of theoriginal liquid (a large amount of liquid) supplied from an externalfree space is drawn into the microchannel through the hole whose innerwall surface is hydrophilic, on the other hand, in PTL 2, a part of theoriginal liquid (a large amount of liquid) supplied from the closedspace sandwiched between the upper substrate and the lower substrate ispushed up from the hole into the free space by the internal pressure ofthe liquid.

On the other hand, Non-PTL 1 discloses a method of hydrophilizing aninner wall surface of a through-hole from an upper layer to a lowerlayer when themicrochannel has two layers and droplets are moved fromthe upper layer (Top Layer) to the lower layer (Bottom Layer). When theinner wall surface of the through-hole is water repellent, the liquiddoes not enter the hole, but the liquid can pass through the hole bymaking the inner wall surface of the hole hydrophilic. As illustrated inthe bottom layer of the Top View illustrated in FIG. 3 of Non-PTL 1, theblue droplet sucked into the hole from the upper layer generally movesto the lower layer, but a part of the droplet is left inside the hole.

CITATION LIST Patent Literature

-   PTL 1: International Publication No. 2017/078059-   PTL 2: JP-A-2008-090066

Non-Patent Literature

-   Non-PTL 1: Micromachines 2015, 6(11), 1655-1674

SUMMARY OF INVENTION Technical Problem

The method of introducing a liquid into a microchannel described in PTL1 aims to tear off a part of the original liquid having a certain largeamount and introduce the liquid into the microchannel. Therefore, in PTL1, no attention has been paid to transporting all of the droplets fromthe microchannel to channels located in other layers or analysisdevices.

PTL 2 also discloses a technique of discharging a part of the originalliquid having a certain large amount as a droplet and using the dropletfor transporting a minute object. However, there is no description abouttransporting all of the droplets from the microchannel to channelslocated in other layers or analysis devices.

Although Non-PTL 1 discloses a technique for moving a droplet from theupper layer to the lower layer, there is room for improvement in that apart of the droplet remains in a hole.

Therefore, the present disclosure provides a technique for moving all ofthe droplets from the microchannel where the droplets have beenintroduced to another layer.

Solution to Problem

In order to achieve the above object, a droplet transport device of thepresent disclosure includes a substrate having a through-hole or arecess, a first electrode provided on the substrate along a surface ofthe substrate and arranged at a position adjacent to the through-hole orthe recess, a plurality of second electrodes provided on the substratealong the surface of the substrate and to which a voltage for moving adroplet introduced on the substrate is applied, a dielectric layercovering the surface of the substrate, the first electrode, and thesecond electrodes, and a water-repellent film provided on an inner wallsurface of the through-hole or the recess, and on the dielectric layer.

Further features relating to this disclosure will become apparent fromthe description of the present specification and the accompanyingdrawings. In addition, the aspects of the present disclosure areachieved and realized by the combination of elements and variouselements, the detailed description below, and the aspects of theappended claims.

The description of the present specification is merely a typical exampleand does not limit the scope of claims or application examples of thepresent disclosure in any sense.

Advantageous Effects of Invention

According to the droplet transport device of the present disclosure, allof the droplet can be moved from the microchannel in which the droplethas been introduced to another layer.

Problems, configurations, and effects other than the above will beclarified by the following description of the embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 10 are schematic perspective views illustrating examples ofan analysis system including a droplet transport device and an analysisdevice.

FIG. 2 is a schematic perspective view illustrating an analysis systemincluding a droplet transport device according to a first embodiment.

FIG. 3A is a cross-sectional view illustrating a configuration in thevicinity of one hole of an EWOD substrate.

FIG. 3B is a plan view illustrating the configuration in the vicinity ofone hole of the EWOD substrate.

FIG. 4 is a cross-sectional view illustrating another configuration inthe vicinity of one hole of the EWOD substrate.

FIG. 5A is a cross-sectional view illustrating a state in which dropletsare supplied from a droplet transport device to a nanopore device.

FIG. 5B is a diagram illustrating current waveforms obtained from fourchannels of the nanopore device.

FIG. 6A is a schematic perspective view illustrating an analysis systemincluding a droplet transport device according to a third embodiment.

FIG. 6B is a cross-sectional view illustrating the analysis systemincluding the droplet transport device according to the thirdembodiment.

FIGS. 7A and 7B are cross-sectional views illustrating a configurationin the vicinity of one well of an EWOD substrate.

FIG. 8 is a schematic diagram illustrating the results of capillaryelectrophoresis of nucleic acids.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the accompanying drawings. In the accompanyingdrawings, functionally the same elements may be displayed with the samereference numerals. The accompanying drawings illustrate specificembodiments and implementation examples in accordance with theprinciples of the present disclosure, but these are for the purpose ofunderstanding the present disclosure and are not used to construe thepresent disclosure in a limited manner. That is, it is necessary tounderstand that the description of the present specification is merely atypical example and does not limit the scope of claims or applicationexamples in any sense.

The various embodiments described below have been described insufficient detail for those skilled in the art to implement the presentdisclosure, but other implementations and embodiments are also possibleand it is possible to change the configuration and structure and replacevarious elements without departing from the scope and spirit of thetechnical ideas of the present disclosure. Therefore, the followingdescription should not be construed as limited thereto.

In each embodiment, as an example of bioanalysis, an example ofanalyzing nucleic acid is illustrated. However, since the presentdisclosure is basically related to the control of a droplet whenanalyzing an analysis target contained in the droplet (whether in adissolved, suspended, or suspended state), what is contained in thedroplet is not limited to nucleic acids, but may be components of bloodor other body fluids. Furthermore, the analysis target is not limited tothose derived from living organisms such as animals and plants and thetechniques of the present disclosure can be similarly applied to thefood industry and various industries. The techniques of the presentdisclosure are applicable as long as the characteristics within thedroplet are preserved by a medium (e.g., air or oil) that isolates thedroplet from external influences. For example, when a sensor of theanalysis device is a pH sensor, it is also applicable to the industrialuse to measure the pH of a droplet under the restriction that thesubstance to be determined for pH in the droplet does not diffuse intoair or oil. On the other hand, when the sensor is a temperature sensor,the amount of heat contained in the minute droplets is easily diffusedto the outside via air or oil (or heat conduction of the substrate), andthus, the technique of the present disclosure is not suitable for suchan application. Even if the analysis target leaks to the isolationmedium to some extent, it is possible to estimate the initialcharacteristics in consideration of the diffusion loss if the speed ofthe leakage is slow. Since the present disclosure relates only to atechnique for controlling a droplet in order to analyze somecharacteristics of the droplet, any analysis targets can be used as longas the characteristic of the droplet is targeted, under theabove-mentioned restrictions.

First Embodiment <Overview of Droplet Transport>

The present embodiment will describe a droplet transport device(sometimes called a “pretreatment module”) and an analysis system usingthe same, for moving all of the droplet from a layer of an EWODmicrochannel, which has been performing operations such as transportingand mixing the introduced droplet, to a layer different therefrom, in astate where minute droplet (specimen droplet, reagent droplet, or thelike) is introduced into the EWOD microchannel. It is assumed that thedroplet introduced into the microchannel is, for example, a droplet thathas been measured at a fixed amount, or a droplet that has been mixed orreacted with a reagent at a predetermined concentration or apredetermined amount. Therefore, it is ideal to utilize all of thedroplet when further reacting with another reagent thereafter, or whenperforming some quantitative analysis thereafter. It is required to useall of the droplet, especially when the liquid should not be wasted atall, such as for a rare droplet such as a specimen that was originallycollected in very small amounts, a droplet containing a dilute analysistarget substance, and a droplet containing the analysis target with lowdetection sensitivity in the analysis and for which whether or not to beable to be detected is important.

Before explaining the features of the droplet transport device of thepresent embodiment, first, in an analysis device including a sensorarray in which a plurality of sensors are arranged in a two-dimensionalarray, an example of a method of supplying droplets to be analyzed froma microchannel located on an upper layer thereof and executing theanalysis will be described.

FIG. 1A is a schematic perspective view illustrating an example of ananalysis system including a droplet transport device 100 and an analysisdevice 10. As illustrated in FIG. 1A, the analysis device 10 (sometimesreferred to as an “analysis module”) has 2×2=4 sensors 11 (sensor array)arranged in an array. The droplet transport device 100 includes an EWODsubstrate 111 and an upper substrate 112 facing each other and amicrochannel 101 (upper layer) is defined by the EWOD substrate 111 andthe upper substrate 112. Further, the EWOD substrate 111 and theanalysis device 10 are arranged so as to face each other and a lowerlayer 102 is defined by the EWOD substrate 111 and the analysis device10.

Water-repellent films (not illustrated) are provided on the uppersurface and the lower surface of the EWOD substrate 111 (the uppersurface and the lower surface of the EWOD substrate 111 arewater-repellent treated). At least a surface of the upper substrate 112facing the EWOD substrate 111 (a surface in the microchannel 101) iswater-repellent. Since a general technique can be employed as the methodfor transporting droplets using the EWOD technique, the description andillustration of the transport control electrode and the dielectric layerof the EWOD substrate 111 will be omitted here.

The EWOD substrate 111 is provided with four holes 113 (through-holes)corresponding to the arrangement of the four sensors 11. That is, theholes 113 are arranged substantially directly above the sensor 11. Theposition of the hole 113 does not have to be exactly directly above thesensor 11 and may be slightly displaced as long as the droplet can besupplied onto the sensor 11 by dropping the droplet from the hole 113.Although FIG. 1A illustrates an example in which the shape of the hole113 is substantially circular, other shapes may be used.

In the analysis method using the analysis system as described above,first, the droplet transport device 100 and the analysis device 10 asdescribed above are prepared, and a target droplet 1 containing thesubstance to be analyzed is introduced from an injection port (notillustrated) into the microchannel 101. Then, the target droplet 1 issplit into four by the droplet splitting operation by EWOD and foursplit droplets 2 are obtained. The target droplet 1 may be, for example,a droplet obtained by an operation such as mixing a sample containing ananalysis target introduced into the microchannel 101 with a reagent.

Next, the split droplets 2 are placed on each sensor 11 by dropping eachof the split droplets 2 from different holes 113 by the droplettransport operation by EWOD. These split droplets 2 can be analyzedsimultaneously by the analysis device 10.

Although not illustrated, the spaces other than the droplets in themicrochannel 101 and the lower layer 102 are filled with a medium forisolating the droplets from each other. This medium is a fluid (liquidor gas) having a specific gravity smaller than that of droplets andphase-separating from water, such as oil (silicone oil, mineral oil, orthe like) and air. As a result, the droplet can fall from the hole 113provided in the microchannel 101 of the upper layer to the lower layer102 under the influence of gravity. When the specific gravity of themedium is larger than the specific gravity of the droplet to betransported (fluorine-based oil, or the like), the analysis system isturned upside down so that the droplets can be supplied to the analysisdevice 10 located in the upper layer from the microchannel 101 locatedin the lower layer.

In the analysis system of FIG. 1A, as the number of arrays of thesensors 11 of the analysis device 10 is increased, the number of dataobtained within the same time increases. For example, when it isnecessary to acquire a large amount of data (inclease n numbers) byincreasing the data acquisition time or increasing the number of dataacquisitions in order to improve the accuracy of analysis, if this canbe simultaneously performed in parallel by the array, as a result,highly accurate results can be obtained in a short time.

FIG. 1B is a schematic perspective view for illustrating anotheranalysis method using the analysis system illustrated in FIG. 1A. In theanalysis method of FIG. 1B, one target droplet is not split by thedroplet transport device 100, but four droplets 3 a to 3 d containingfour different analysis targets are supplied to the analysis device 10and analyzed at the same time. This quadruples the analysis efficiency.

Note that, when the 2×2=4 sensor arrays illustrated in FIGS. 1A and 1Bare used, four droplets can be also supplied by accessing from theperipheral portion of the four sensors 11. Thus, by supplying thedroplets from the microchannel 101 in the upper layer to the analysisdevice 10 in the lower layer through the holes 113 (by transporting thedroplets to another layer), the effect of making the droplet transportdevice 100 compact (reducing the footprint of the pretreatment module)may not be so great.

However, as the number of sensor arrays increases, the effect of makingthe droplet transport device compact increases. For example, when 4×4=16sensor arrays are used, if the configuration for transporting dropletsto other layers is not used, it is especially difficult to access thefour sensors located inside the sensor array and to supply the droplets.In order to reliably supply the droplets to the four inner sensors, itis necessary to widen the pitch of the sensor array and secure a gap asa passage for the droplets. However, widening the pitch of the sensorarray hinders the high integration and miniaturization of the analysisdevice. Therefore, it is important to arrange the droplets in an arraywhile supplying the droplets from the microchannel located in the upperlayer to the analysis device located in the lower layer forcompactification.

FIG. 10 is a schematic perspective view illustrating an example ofanother analysis system including a droplet transport device 200 and ananalysis device 20. The analysis device 20 has 4×4=16 sensors 21arranged in an array. The droplet transport device 200 includes EWODsubstrates 211 a and 211 b and an upper substrate 212. The uppersubstrate 212 and the EWOD substrate 211 a define a microchannel 201 ain the uppermost layer. The EWOD substrates 211 a and 211 b define amicrochannel 201 b in the intermediate layer. A bottom layer 202 isdefined by the EWOD substrate 211 b and the analysis device 20.

The EWOD substrate 211 a is provided with four holes 213 a(through-holes) located substantially directly above the four (2×2)sensors 21 located in the center of the sensor array. The EWOD substrate211 b is provided with 16 holes 213 b (through-holes) locatedsubstantially directly above the 16 sensors 21 of the analysis device20. With such a configuration, droplets can be dropped from themicrochannel 201 a in the uppermost layer so as to pass through the fourholes 213 a and the four holes 213 b located in the center of the 16holes 213 b and can be supplied onto the four sensors 21 located in thecenter of the analysis device 20. Further, on the 12 sensors 21 locatedon the peripheral edge of the sensor array, droplets can be dropped fromthe microchannel 201 b of the intermediate layer so as to pass throughthe holes 213 b located substantially directly above the 12 sensors 21,whereby the droplets can be supplied. By supplying the droplets in thisway, the droplet transport device 200 and the analysis device 20 havinga small footprint and compact size can be realized without widening thepitch of the analysis device 20.

As described above, by providing holes in the EWOD substrateconstituting the layer of the microchannel and supplying droplets toother layers through the holes, it is possible to be stored in a compactstacking module (analysis system) having a small footprint withoutwidening the pitch between the sensors. As a result, more sensors can beplaced in the same footprint, leading to improved data accuracy andimproved data acquisition efficiency. Further, by using the droplettransport device having the above configuration, it becomes easy tosupply the droplets to each sensor of the analysis device.

<Configuration Example of Droplet Transport Device According to PresentEmbodiment>

FIG. 2 is a schematic perspective view illustrating an analysis systemincluding a droplet transport device 300 and the analysis device 20according to the first embodiment. As illustrated in FIG. 2, theconfiguration of the droplet transport device 300 is almost the same asthe configuration of the droplet transport device 200 illustrated inFIG. 1C, but the difference is that an EWOD substrate 311 a has threeholes 314 a (through-holes) and an operation unit 320 for preparing thesplit droplets 2 to be supplied to the analysis device 20. The holes 314a are arranged along the lateral direction of the EWOD substrate 311 a.The operation unit 320 includes a transport unit 321, a stirring unit322, a reaction unit 323, and a splitting unit 324, which are arrangedin this order in the direction toward the hole 313 a (longitudinaldirection of the EWOD substrate 311 a).

The target droplet 1 containing the nucleic acid to be analyzed issupplied to the transport unit 321 and the target droplet 1 istransported to the stirring unit 322 by the droplet operation in thetransport unit 321. Although not illustrated, a reagent droplet istransported to the stirring unit 322 from another pathway, and thetarget droplet 1 and the reagent droplet are mixed and stirred in thestirring unit 322. The mixed droplet is transported to the reaction unit323. The reaction unit 323 is provided with a temperature controlmechanism (not illustrated), and the nucleic acid in the mixed dropletis replicated by moving the mixed droplet on the reaction unit 323. Forthe replication reaction, PCR that is generally widely used for nucleicacid analysis may be used and in the reaction unit 323, the surface ofthe EWOD substrate 311 a is temperature-controlled so that thetemperature conditions are suitable for the PCR reaction. After that,the droplet containing the replicated nucleic acid is transported to thesplitting unit 324 and is split into four split droplets 2 by thedroplet operation in the splitting unit 324.

The configuration of the operation unit 320 can be appropriately changedaccording to the analysis target and the analysis content. When it isnot necessary to control the temperature of the droplets supplied to theanalysis device 20 or mix the droplets with a reagent, the operationunit 320 may not be provided.

The configuration of the analysis device 20 is the same as thatillustrated in FIG. 10. As described above, in the present embodiment,as an example, nucleic acid analysis is performed by 4×4=16 sensorsarranged in an array. Therefore, 16 droplets corresponding to the numberof sensors of the analysis device 20 are transported by the droplettransport device 300. The amount corresponding to 4 droplets out of 16droplets is ¼ of the original target droplet 1. Therefore, the originaltarget droplet 1 is first split into four by the splitting unit 324, oneof the split droplets 2 is left in the microchannel 301 a of theuppermost layer, and the remaining three split droplets 2 are droppedinto the three holes 314 a and moved to the microchannel 301 b of theintermediate layer. The split droplet 2 left in the microchannel 301 ais further split into four on the microchannel 301 a and supplied fromthe four holes 313 a to the analysis device 20 by passing through theholes 313 b provided in the microchannel 301 b of the intermediatelayer. The three split droplets 2 introduced into the microchannel 301 bare each split into four droplets (12 in total) on the microchannel 301b and are supplied from 12 holes 313 b out of the 16 holes 313 b locatedat the peripheral edge to the analysis device 20 located in thelowermost layer 302, respectively.

In this way, since the split droplet 2 falls from the hole 314 a and thedroplet obtained by further splitting the split droplet 2 falls from thehole 313 a, the size of the hole 314 a is formed larger than the size ofthe hole 313 a.

<Hole Configuration>

As a result of diligent studies of the present inventors to drop all ofthe droplets from the holes 313 a and 314 a provided in the EWODsubstrate 311 a and the holes 313 b provided in the EWOD substrate 311b, it has been found that it is effective to provide electrodes fordrawing droplets on the edges of the holes and to treat the inner wallsurfaces of these holes with water repellent treatment.

FIG. 3A is a cross-sectional view illustrating a configuration in thevicinity of one hole 314 a of the EWOD substrate 311 a. Hereinafter,only the hole 314 a of the EWOD substrate 311 a illustrated in FIG. 3Awill be described as a representative. Note that, the followingdescription also applies to the hole 313 a of the EWOD substrate 311 aand the hole 313 b of the EWOD substrate 311 b.

As illustrated in FIG. 3A, the EWOD substrate 311 a includes a pull-inelectrode 330 (first electrode) provided adjacent to the hole 314 a andtransport control electrodes 340 (a plurality of second electrodes) fortransporting the split droplet 2 by EWOD. The pull-in electrode 330 andthe transport control electrode 340 are arranged along the upper surfaceof the EWOD substrate 311 a. In reality, the EWOD substrate 311 a isformed such that the pull-in electrode 330 and the transport controlelectrode 340 are arranged on the substrate, a dielectric layer isprovided so as to cover those electrodes, and a water-repellent film 350is provided on the dielectric layer, but the illustration is omitted forthe sake of simplicity.

The pull-in electrode 330 is connected to a power supply 332 by wiring.The application of the voltage to the pull-in electrode 330 can beswitched on or off by operating a contact switch 331 provided in themiddle of the wiring. The contact switch 331 may be switched manually orautomatically. When the contact switch 331 is automatically controlled,for example, a switch drive mechanism (not illustrated) and a controller(not illustrated) for controlling the switch drive mechanism and thepower supply 332 are provided, and the application of the voltage to thepull-in electrode 330 can be controlled by the controller. The contactswitch 331 is controlled to be turned on at least when the dropletreaches the pull-in electrode 330. Similarly, the transport controlelectrode 340 is also connected to a power source for applying the EWODcontrol voltage by wiring.

The water-repellent film 350 is provided on the upper surface of theEWOD substrate 311 a (that is, on the dielectric layer) and the innerwall surface of the hole 314 a. A water-repellent film (not illustrated)is also provided on the lower surface of the EWOD substrate 311 a. Sincethe inner wall surface of the hole 314 a is water-repellent in this way,all of the split droplet 2 can be transported to the lower layer(microchannel 301 b of the intermediate layer) without leaving a part ofthe split droplet 2 inside the hole 314 a. As the water-repellent film350, a known water-repellent material such as a fluororesin such aspolytetrafluoroethylene or a silicone resin can be used.

FIG. 3A illustrates an example in which the holes 314 a are providedperpendicular to the surface of the EWOD substrate 311 a but the shapeof the holes 314 a is not limited thereto. For example, the upper endportion of the hole 314 a may be processed into a tapered shape (a shapein which the upper end portion of the hole 314 a is rounded). The hole314 a can be formed and processed by, for example, machining, molding,etching, or the like, depending on the material and characteristics ofthe EWOD substrate 311 a.

<Area of Electrode>

The contact area of the split droplet 2 with respect to the EWODsubstrate 311 a may be an area that can contact two adjacent transportcontrol electrodes 340 when an EWOD control voltage is applied to thetransport control electrodes 340. The contact area of the split droplet2 with respect to the EWOD substrate 311 a may occupy an area largerthan the area of one transport control electrode 340, or may cover aplurality of transport control electrodes 340. In other words, the size(volume) of the split droplet 2 can be determined so as to have theabove-mentioned contact area according to the area of the transportcontrol electrode 340.

By setting the area of the pull-in electrode 330 to ½ or less of thearea of the transport control electrode 340, the split droplet 2 can beeasily introduced into the hole 314 a. At this time, the contact switch331 is in the ON state. FIG. 3A illustrates a configuration in which thearea of the pull-in electrode 330 is set to about ½ of the area of thetransport control electrode 340. As illustrated in FIG. 3A, since thearea of the pull-in electrode 330 is about ½ of the area of thetransport control electrode 340, apart of the split droplet 2 protrudestoward the hole 314 a. The gravity and surface tension due to thewater-repellent film 350 are applied to this part of the split droplet2, the entire split droplet 2 can be drawn into the hole 314 a.

FIG. 3B is a plan view illustrating a configuration in the vicinity ofone hole 314 a of the EWOD substrate 311 a. FIG. 3B illustrates fourtypes of examples (pull-in electrodes 330 a to 330 d) in which thepull-in electrode 330 is viewed from above. The pull-in electrode 330 ahas a width of about ½ of the width of the transport control electrode340. As described above, the split droplet 2 can be introduced into thehole 314 a by the pull-in electrode 330 a. Alternatively, for example,even when a pull-in electrode 330 b having a shape slightly surroundingthe hole 314 a or a pull-in electrode 330 c surrounding the hole 314 ain a ring shape is used, the split droplet 2 can be smoothly drawn intothe hole 314 a. As described above, it is appropriate that the pull-inelectrode 330 is as small as about ½ of the transport control electrode340. Strictly speaking, smoother pull-in can be realized by devising theshape. Note that, the pull-in electrode 330 having an area of about ½ ofthat of the transport control electrode 340 is still effective. Sincethe pull-in electrode 330 is for giving an action of pulling the dropletof the transport control electrode 340 into the hole 314 a, aconfiguration is effective in which the pull-in electrode 330 isarranged next to the transport control electrode 340 as in the pull-inelectrodes 330 a to 330 c, and the hole 314 a is at the tip of thepull-in electrode. If the width of the electrode on the transportcontrol electrode 340 side (left side of the hole 314 a) is too narrowlike the pull-in electrode 330 d, a sufficient pull-in force is notgenerated and it is difficult to enter the hole 314 a. The pull-inelectrode 330 d has a certain electrode area on the other side of thehole 314 a (the right side of the hole 314 a), but since it is locatedon the other side of the hole 314 a, it does not sufficiently contributeto the pull-in.

As described above, it has been described that it is effective toprovide the pull-in electrode 330 adjacent to the hole 314 a in order todrop the split droplet 2 to the lower layer. Further, it will bedescribed below that the pull-in electrode can be provided not only onthe surface of the EWOD substrate but also along the inner wall surfaceof the hole.

FIG. 4 is a cross-sectional view illustrating another configuration inthe vicinity of one hole 314 a of the EWOD substrate 311 a. Asillustrated in FIG. 4, in this configuration example, a pull-inelectrode 333 (third electrode) along the inner wall surface of the hole314 a is provided in addition to the configuration illustrated in FIG.3A. That is, the pull-in electrode 333 is provided on the EWOD substrate311 a so as to face the hole 314 a via the water-repellent film 350 inparallel with the inner wall surface of the hole 314 a. The position ofthe pull-in electrode 333 (distance between the inner wall surface ofthe hole 314 a and the pull-in electrode 333) is not particularlylimited as long as the surface energy on the inner wall surface of thehole 314 a can be changed.

The size of the pull-in electrode 333 in the direction parallel to theinner wall surface of the hole 314 a is not limited, but by increasingthe size of the pull-in electrode 333, in particular, by providing thepull-in electrode 333 over the entire length of the inner wall surfaceof the hole 314 a, the split droplet 2 can be more easily drawn into thehole 314 a. Although FIG. 4 illustrates a configuration in which thepull-in electrode 330 and the pull-in electrode 333 are in contact witheach other, these pull-in electrodes may be arranged apart from eachother.

By making an area of the pull-in electrode 333 along the inner wallsurface of the hole 314 a larger than the area of the pull-in electrode330 along the surface of the EWOD substrate 311 a, the split droplet 2can be more easily drawn into the hole 314 a. FIG. 4 illustrates aconfiguration in which the area of the pull-in electrode 333 is largerthan the area of the pull-in electrode 330.

When the pull-in electrode 333 is provided, even if the area of thepull-in electrode 330 is larger than ½ of the area of the transportcontrol electrode 340, the split droplet 2 can be easily drawn into thehole 314 a.

From the above, the area of the pull-in electrode 330 is set to ½ orless of the area of the transport control electrode 340, and the area ofthe pull-in electrode 333 is made larger than the area of the pull-inelectrode 330, whereby the introduction of the split droplet 2 into 314a can be ensured.

<Application of Voltage>

The present inventors examined the application of voltage to the pull-inelectrode 330 in order to introduce all of the split droplet 2 into thehole 314 a. As a result, it has been found that the split droplet 2 canbe drawn into the hole 314 a by continuously applying a voltage to thepull-in electrode 330 until the split droplet 2 reaches the hole 314 a.

If a high voltage (for example, 30 V to 100 V) is continuously appliedto the pull-in electrode 330, the split droplet 2 may be trapped in thehole 314 a. Therefore, after being trapped, the split droplet 2 can bedropped from the hole 314 a by turning off the contact switch 331 tostop the voltage application.

Further, it has been found that in any voltage range in which the splitdroplet 2 can be moved, after applying a voltage to the pull-inelectrode 330, when the voltage is continuously applied until the splitdroplet 2 reaches the about ½ position of the distance between thecenter of the transport control electrode 340 adjacent to the pull-inelectrode 330 and the center of the upper end of the hole 314 a, and theapplication of the voltage is stopped thereafter, the split droplet 2can be reliably introduced into the hole 314 a.

As described above, the split droplet 2 can be introduced into the hole314 a by turning on the application of the voltage to the pull-inelectrode 330 for a certain period of time and then turning off (GND)the voltage application.

<Hole Size>

When the planar shape of the hole 314 a is substantially circular, bymaking the diameter of the hole 314 a larger than the diameter of thesplit droplet 2 (the diameter calculated by assuming a sphere from thevolume of the split droplet 2), the split droplet 2 is drawn into thehole 314 a so as to slide down. When the diameter of the hole 314 a ismade smaller than the diameter of the split droplet 2, the split droplet2 becomes difficult to enter because the inner wall surface of the hole314 a is water repellent. In this case, by increasing the voltageapplied to the pull-in electrode 330 (for example, 30 V to 100 V), thesplit droplet 2 can be deformed and enter the hole 314 a. Note that, itis presumed that the viscosity of the split droplet 2 and therestriction of the voltage value so as not to cause dielectric breakdownoccur.

<Technical Effect>

As described above, in the droplet transport device according to thefirst embodiment, the EWOD substrate has a hole for supplying thedroplet to the lower layer and the inner wall surface of the hole istreated with water repellent treatment. In addition, the EWOD substrateincludes a pull-in electrode at a position adjacent to the hole. Withsuch a configuration, all of the droplet can be supplied to the lowerlayer through the holes without leaving a part of the droplet on theEWOD substrate. Therefore, when arranging the analysis device having thesensor array under the EWOD substrate, it is not necessary to widen thepitch between the sensors to provide the droplet passage. As a result,since the array can be densely integrated on a small footprint, thedroplet transport device and the analysis device can be miniaturized andanalysis can be performed with high throughput.

Second Embodiment

In the first embodiment, an analysis system for performing analysis bysupplying droplets from a droplet transport device provided with holesin the EWOD substrate to a sensor array located in a lower layer hasbeen described. The droplet transport device is not limited to thesensor array and can be used in combination with an analysis devicehaving another configuration. Therefore, in a second embodiment, ananalysis system for supplying a droplet from the droplet transportdevice to a nanopore device for analyzing nucleic acid will bedescribed. As the droplet transport device used in this embodiment, thesame droplet transport device 300 as illustrated in FIG. 2 will beemployed and the description thereof will be omitted.

FIG. 5A is a cross-sectional view illustrating a state in which dropletsare supplied from the droplet transport device 300 to a nanopore device30 (analysis device). The configuration of the droplet transport device300 is the same as that of the droplet transport device 300 of the firstembodiment illustrated in FIG. 2. FIG. 5A illustrates the vicinity ofone hole 313 b of the EWOD substrate 311 b constituting the intermediatelayer of the droplet transport device 300. A droplet 4 supplied from theintermediate layer to the nanopore device 30 in the lowermost layer isobtained by splitting each of the above-mentioned four split droplets 2into four. As described above, the nucleic acid contained in one targetdroplet 1 is amplified by the operation unit 320, then split into foursplit droplets 2, which are further split into four droplets 4,respectively. Therefore, the obtained 16 droplets 4 contain the samenucleic acid.

The nanopore device 30 includes a substrate 34 on which a membrane 32having pores 31 is formed, an upper electrode 36, and a lower electrode35. The membrane 32 has a thickness on the order of nanometers, forexample, and the pores 31 are formed on the order of nanometers. Thesubstrate 34 has a tapered shape around the membrane 32 on the uppersurface thereof and can hold the droplet 4 that has fallen from the hole313 b. Since the periphery of the droplet 4 is filled with a fluid thatis phase-separated from the droplet, the droplet 4 itself constitutes aliquid tank (first liquid tank). In the nanopore device 30, a secondliquid tank is formed on the lower surface side of the substrate 34, andthe second liquid tank holds an aqueous electrolyte solution 33. Theupper electrode 36 comes into contact with the droplet 4 constitutingthe first liquid tank, and the lower electrode 35 comes into contactwith the aqueous electrolyte solution 33 supplied to the second liquidtank. The current flowing between the upper electrode 36 and the lowerelectrode 35 is measured by an ammeter (not illustrated). When thenucleic acid molecule in the droplet 4 passes through the pore 31, thecurrent changes according to the base sequence of the nucleic acidmolecule, so that the base sequence can be decoded from thecharacteristics of this change.

Although only one channel is illustrated in FIG. 5A, it is assumed thatthe substrate 34 is provided with 4×4=16 membranes 32 in an array toform 16 channels. The droplet transport device 300 and the nanoporedevice 30 are arranged so that the holes 313 b of the EWOD substrate 311b are located substantially directly above the membrane 32,respectively. As described above, since the 16 droplets 4 contain thesame sample, the same data can be acquired simultaneously on 16channels. For example, when comparing with the case where the signaloutput from the ammeter is weak and the data with uncertainty isrepeatedly acquired 16 times, the data acquisition efficiency isimproved 16 times.

FIG. 5B is a diagram illustrating current waveforms obtained from 4channels out of the 16 channels of the nanopore device 30. Asillustrated in FIG. 5B, although noise is observed in the currentwaveforms, the current waveforms of the four channels show the samebehavior and show some features of the same base sequence.

In order to actually decode the base sequence of nucleic acid, when datais acquired only with a one-channel sensor (nanopore device), the mostprobable waveform can be clarified by acquiring a large number of dataof nucleic acid molecules having the same sequence and analyzing theplurality of data. On the other hand, in the above-mentioned 16-channelmulti-array measurement, 16 series of data can be acquired at the sametime, and the data can be efficiently acquired and the accuracy ofdecoding can be improved from the analysis. If the noise of the signalobtained from one channel is reduced to make the data clearer withtechnological progress, and thus, the data on one channel is sufficientto decode the base sequence, it is needless to say that the 16 channelscan be used to acquire data from different base sequences. In that case,the target droplet 1 containing the replicated nucleic acid molecules ofthe same sequence is not split into 16 in the droplet transport device300 as described with reference to FIG. 2, but the 16 types of dropletsmay be subjected to pretreatment (mixing or reaction with a reagent, orthe like) with the same method and supplied to a 16-channel arraysensor. The concept is the same as that illustrated in FIG. 1B as anexample when four droplets are used.

<Technical Effect>

As described above, the second embodiment described the method in whichthe droplet 4 is supplied from the droplet transport device 300 to eachchannel of the multi-array nanopore device 30, and the base sequence ofthe nucleic acid is analyzed. Similar to the first embodiment, the innerwall surfaces of the holes 313 a and 215 a provided in the EWODsubstrate 311 a of the droplet transport device 300 and the inner wallsurface of the hole 313 b provided in the EWOD substrate 311 b arewater-repellent and the pull-in electrode 330 for drawing the dropletinto these holes is provided. As a result, droplets can be easily andreliably supplied to each channel of the nanopore device 30, and thus,the efficiency and accuracy of analysis can be improved.

Third Embodiment

In the first and second embodiments, a droplet transport device forsupplying droplets from a hole provided in a microchannel to a sensorarray (analysis device) located in a lower layer has been described. Asthe analysis device that performs analysis using droplets to beanalyzed, not only those mounted on a plane such as a sensor array, butalso analysis devices having other geometric shapes such as acylindrical tubular capillary array are widely used. Therefore, in athird embodiment, a droplet transport device capable of deliveringdroplets to the capillary array analysis device is proposed.

FIG. 6A is a schematic perspective view illustrating an analysis systemincluding a droplet transport device 400 and an analysis device 40according to the third embodiment. As illustrated in FIG. 6A, thedroplet transport device 400 includes an EWOD substrate 411 and an uppersubstrate 412 facing each other, and a microchannel 401 is defined bythe EWOD substrate 411 and the upper substrate 412.

The EWOD substrate 411 is provided with four wells 413 (recesses) fortrapping droplets 5. The wells 413 are arranged along the lateraldirection of the EWOD substrate 411. The upper substrate 412 is providedwith four holes 414 located substantially directly above the wells 413.

The analysis device 40 includes four capillaries 41, a light source thatemits excitation light 42 in the arrangement direction of thecapillaries 41 (not illustrated), a detector that detects fluorescence43 emitted from the capillaries 41 (not illustrated), and othernecessary optical systems. When such an analysis device 40 is used, thedroplet 5 containing a fluorescence-labeled analysis target can beintroduced into the capillary 41 and irradiated with excitation light 42to detect the fluorescence 43 from the analysis target for analysis. Itis also possible to irradiate the capillary 41 with incident light 44and measure its absorption 45 (transmitted light).

When performing analysis using the droplet transport device 400 and theanalysis device 40 of the present embodiment, first, necessaryoperations such as mixing and reaction with a reagent are performed onthe droplet 5 containing the analysis target in the microchannel 401 oroutside the microchannel 401, and the droplet 5 is transported to thewell 413 and dropped by the operation on the EWOD substrate 411. Afterthat, the capillary 41 is inserted into the hole 414 and introduced intothe well 413. As a result, the droplet 5 can be delivered into thecapillary 41.

The number of wells 413 is not limited to four and the columns of wells413 are not limited to one column. For example, the arrangement of thewells 413 may be an array arrangement of a plurality of rows×a pluralityof columns as long as the pitch of the capillary 41 introduced into thewell 413 does not need to be widened.

FIG. 6B is a schematic cross-sectional view illustrating how the droplet5 is introduced into the capillary 41. In FIG. 6B, only the vicinity ofthe tip portion of one capillary 41 is illustrated. Further, theillustration of the upper substrate 412 is omitted. When the droplet 5is sucked into the capillary 41 and electrophoresed, a voltage isapplied to the tip of the capillary 41 to form an electric field.

The left diagram of FIG. 6B illustrates a configuration in which thedroplet 5 is transported to the tip portion of the capillary 41 on theEWOD substrate 420 (on a water-repellent film 450) having no well 413and sucked up. In such a configuration, a transport control electrode440 of the EWOD substrate 420 and the tip of the capillary 41 are inclose proximity to each other in a geometrical arrangement. On the otherhand, by increasing the distance between the transport control electrode440 and the tip of the capillary 41, it is possible to prevent damage tothe droplet transport device 400 and the capillary 41 due to dielectricbreakdown. Therefore, as illustrated in the center diagram and the rightdiagram of FIG. 6B, the influence of the transport control electrode 440can be reduced by temporarily dropping the droplet 5 into the well 413and then sucking the droplet 5 into the capillary 41.

Further, in the configuration illustrated on the left diagram of FIG.6B, since the droplet 5 has a flat shape sandwiched between the uppersubstrate 412 and the EWOD substrate 420, it is not easy to suck up thedroplet 5 by the capillary 41. The right diagram of FIG. 6B illustratesa forward taper shape in which the well 413 narrows toward the bottom.With such a shape, the droplet 5 can be collected at the center of thetip of the capillary 41. Further, since the well 413 is tapered towardthe bottom, the height of the droplet 5 contained in the bottom of thewell 413 is higher than that when the diameter of the well 413 isuniform (in the center diagram of FIG. 6B). Therefore, it can be saidthat the introduction of the droplet 5 into the capillary 41 becomeseasier.

The inner wall surface and the bottom surface of the well 413 are formedby the water-repellent film 450, but only the inner wall surface may becomposed of the water-repellent film 450. The well 413 is provided withthe water-repellent film 450 so as to form a through-hole or a recess inthe EWOD substrate 411, for example, by etching or dielectric breakdownaccording to the material and characteristics of the EWOD substrate 411,and then to form the bottom of the through-hole. Alternatively, the well413 can be formed by providing the water-repellent film 450 on the innerwall surface of the recess, or on the inner wall surface and the bottomsurface thereof.

In the center diagram and the right diagram of FIG. 6B, the depth of thewell 413 is larger than the thickness of the EWOD substrate 411, but thedepth of the well 413 is not limited thereto and the depth of the well413 may be less than or equal to the thickness of the EWOD substrate411.

The analysis system for performing analysis by combining the droplettransport device 400 that introduces the droplet 5 into the well 413 andthe analysis device 40 including the capillary 41 for electrophoresishas been described above. On the other hand, for example, adopting aconfiguration (pretreatment module+electrophoresis tube integratedmounting type module) having a structure in which a capillary is builton a flat substrate and in which light is incident from the top, bottom,left, and right of the substrate to perform observation may not beimpossible. However, for example, when analyzing a nucleic acid as asample, cross-contamination in the pretreatment module must be strictlyprohibited. For example, when the pretreatment involves a nucleic acidreplication reaction such as PCR (polymerase chain reaction), there is arisk that even a very small amount of nucleic acid not to be analyzedwill be replicated and the analysis result will be completely wrong. Toavoid this, the pretreatment module can be disposable. On the otherhand, since nucleic acid replication does not occur in theelectrophoresis tube used for analysis, the electrophoresis tube can beused repeatedly by washing the electrophoresis tube and resetting thehistory. For these reasons, it is not a good idea from the viewpoint ofanalysis cost to integrally mount a high-cost electrophoresis tube on adisposable pretreatment module and dispose of the electrophoresis tube,which is a precision optical component, every time. Therefore, like thedroplet transport device 400 of the present embodiment, a method ofdelivering droplets from a disposable pretreatment module manufacturedat a low manufacturing cost to a reusable electrophoresis tube can beadopted.

<Configuration of Wells>

FIG. 7A is a cross-sectional view illustrating a configuration in thevicinity of one well 413 of the EWOD substrate 411. The left diagram ofFIG. 7A illustrates a state before the droplet 5 is dropped into thewell 413, and the right diagram illustrates a state in which the droplet5 has been dropped into the well 413. As illustrated in FIG. 7A, thebottom of the well 413 can be curved.

As illustrated in FIG. 7A, the EWOD substrate 411 includes a pull-inelectrode 430 provided adjacent to the well 413 and a transport controlelectrode 440 for transporting the droplet 5 by applying an EWOD controlvoltage. The pull-in electrode 430 and the transport control electrode440 are arranged along the upper surface of the EWOD substrate 411. Inthe example illustrated in FIG. 7A, the pull-in electrode 430 is notprovided inside the well 413, and the area of the pull-in electrode 430is about ½ of the area of the transport control electrode 440. Thewiring, power supply, and contact switch for applying a voltage to thepull-in electrode 430 are the same as those in the first embodiment(FIGS. 3A and 3B). Further, the EWOD substrate 411 may be provided witha pull-in electrode (third electrode) (not illustrated) along the innerwall surface of the well 413.

A dielectric layer 460 is provided on the upper surface of the EWODsubstrate 411 and the water-repellent film 450 is further provided onthe upper surface thereof. The water-repellent film 450 is also providedon the inner wall surface and the bottom surface of the well 413.

<Introduction of Droplet into Capillary>

As illustrated in the left diagram of FIG. 7A, first, the droplet 5 isdropped into the well 413. At this time, as described in the firstembodiment, the droplet 5 can be drawn into the well 413 by applying avoltage to the pull-in electrode 430 for a certain period of time. Sincethe inner wall surface of the well 413 is water-repellent up to thebottom, the droplet 5 can reach the bottom without stopping on the innerwall surface in the middle of the well 413. Further, since the bottom ofthe well 413 is curved, the droplet 5 can be contained in the center ofthe bottom of the well 413.

In order to drop the droplet 5 to the bottom of the well 413, thewater-repellent film 450 may be provided on at least the inner wallsurface. That is, the bottom of the well 413 may be a hydrophilicsurface.

After introducing the droplet 5 into the well 413, the capillary 41 isinserted into the well 413 as illustrated in the right diagram of FIG.7A. The material of the capillary 41 is typically glass and the tipsurface is a hydrophilic surface. Therefore, by bringing the droplet 5into contact with the tip portion of the capillary 41, the capillary 41can reliably access the droplet 5.

For example, even when the tip surface of the capillary 41 remainshydrophilic and the outer surface is water-repellent treated with aresin coating, the tip surface of the capillary 41 can come into contactwith the droplet 5. Although the shape of the meniscus of the droplet 5with respect to the outer surface is different from the case where theouter surface of the capillary 41 is also hydrophilic, the droplet 5 canbe easily sucked into the capillary 41 by appropriately adjusting theforward taper shape inside the well 413, the diameter of the bottom ofthe well 413, the amount (height) of the droplet 5 to be introduced intothe well 413, and the like.

FIG. 7B is a cross-sectional view for illustrating a method of suckingthe droplet 5 into the capillary 41. As illustrated in the left diagramof FIG. 7B, by immersing the capillary 41 in the droplet 5, for example,it can be used for general chromatography analysis.

On the other hand, when electrophoresis (the substance in the droplet 5is electrophoresed and analyzed in the capillary 41 by an electricfield) is used, as illustrated in the right diagram of FIG. 7B, theanalysis device 40 is provided with wiring, a cutoff switch 46, and apower supply 47 for applying a voltage to both ends of the capillary 41.Further, the droplet transport device 400 is provided with wiring, apower supply 432, and a cutoff switch 431 for applying a predeterminedvoltage to the pull-in electrode 430 and the transport control electrode440, respectively.

For example, when a potential difference of 10 kV is provided betweenthe tip portion and the upper end portion of the capillary 41, −10 kVcan be applied to the tip portion to make the upper end portion GND, orthe tip portion can be made GND by applying 10 kV to the upper endportion. How to apply the voltage can be appropriately selectedaccording to the design. For example, when a configuration in which theupper end portion is electrophoresed as GND is preferable in terms ofdesign, in consideration of the breakdown voltage (breakdown distancewith respect to 10 kV) of the medium (fluid) isolating the droplet 5,design requirements such as providing a sufficient distance between thetip of the capillary 41, and the transport control electrode 440 and thepull-in electrode 430 by increasing the depth of the well 413 providedon the EWOD substrate 411 or increasing the opening diameter of the well413 are required. As described above, since the droplet 5 can be easilyintroduced into the well 413 by making the diameter of the droplet 5smaller than the diameter of the well 413, there is no problem inpulling in the droplet 5 even if the well 413 is designed to be large.Further, since the water-repellent film 450 is provided on the innerwall surface of the well 413, the droplet 5 reaches the bottom of thewell 413 even when the well 413 becomes deep. The design of the depthand diameter of the well 413 also depends on the dielectric breakdownstrength of the droplet isolation medium (fluid) used.

Further, the dielectric breakdown of the pull-in electrode 430 and thetransport control electrode 440 can be prevented by switching betweenthe application of the voltage to the electrodes and the application ofthe voltage to the capillary by using the cutoff switches 431 and 46having a high withstand voltage. The switching of the cutoff switches431 and 46 and the control of the power supplies 432 and 47 can beexecuted by a controller (not illustrated). The controller controls thecutoff switch 46 to be turned off so that no voltage is applied to bothends of the capillary 41 until the droplet 5 is introduced into the well413. Further, when a voltage is applied to both ends of the capillary41, the cutoff switch 431 is controlled to be turned off.

<Nucleic Acid Electrophoresis>

FIG. 8 is a schematic diagram illustrating the results of capillaryelectrophoresis of nucleic acids using the analysis system (FIGS. 6A and6B) according to the present embodiment. The left diagram and the centerdiagram of FIG. 8 illustrate that the nucleic acid profiles of twosamples among the three samples acquired in some scene matched. Theright diagram of FIG. 8 illustrates that the nucleic acid profile of onesample did not match the other two.

The result of the electrophoresis can be obtained, for example, by theoperation described with reference to FIGS. 6A and 6B. That is, withrespect to the three samples acquired in some scene, operations such asmixing and reaction with a reagent is performed in the microchannel 401to prepare droplets to be analyzed, and each is introduced into the well413. After that, the capillary 41 is inserted into the well 413 and avoltage is applied to both ends of each capillary 41 to electrophore thedroplet in the capillary 41 to obtain a nucleic acid profile of thesample. As described above, in the droplet transport device 400, sincethe inner wall surface of the well 413 is water-repellent and thepull-in electrode 430 is provided close to the well 413, all of thedroplet can be introduced into the well 413. As a result, even when onlya very small amount of sample can be obtained, it can be introduced intothe capillary 41 (analysis device 40), and thus, the accuracy ofanalysis can be ensured. Further, by providing a plurality of wells 413,analysis of a plurality of samples can be performed at the same time, sothat the analysis result can be obtained quickly.

[Modification]

The present disclosure is not limited to the above-described embodimentsand includes various modifications. For example, the above-describedembodiments have been described in detail in order to explain thepresent disclosure in an easy-to-understand manner and does notnecessarily include all of the configurations described. In addition, apart of one embodiment can be replaced with the configuration of anotherembodiment. It is also possible to add the configuration of anotherembodiment to the configuration of one embodiment. It is also possibleto add, delete, or replace a part of the configuration of anotherembodiment with respect to apart of the configuration of eachembodiment.

REFERENCE SIGNS LIST

-   -   100 to 400 . . . droplet transport device    -   101, 201 a, 201 b, 301 a, 301 b, 401 . . . microchannel    -   102 . . . lower layer    -   202, 302 . . . bottom layer    -   111, 211 a, 211 b, 311 a, 311 b, 411 . . . EWOD substrate    -   112, 212, 312, 412 . . . upper substrate    -   320 . . . operation unit    -   330, 333, 430 . . . pull-in electrode    -   340, 440 . . . transport control electrode    -   331 . . . contact switch    -   332 . . . power supply    -   350, 450 . . . water-repellent film    -   460 . . . dielectric layer    -   431, 46 . . . cutoff switch    -   432, 47 . . . power supply

1. A droplet transport device comprising: a substrate including athrough-hole or a recess; a first electrode provided on the substratealong a surface of the substrate and arranged at a position adjacent tothe through-hole or the recess; a plurality of second electrodesprovided on the substrate along the surface of the substrate and towhich a voltage for moving a droplet introduced onto the substrate isapplied; a dielectric layer covering the surface of the substrate, thefirst electrode, and the second electrodes; and a water-repellent filmprovided on an inner wall surface of the through-hole or the recess, andon the dielectric layer.
 2. The droplet transport device according toclaim 1, wherein an area of the first electrode is ½ or less of an areaof the second electrode.
 3. The droplet transport device according toclaim 2, wherein the first electrode has a shape that surrounds at leasta part of a periphery of the through-hole or the recess, and whose widthon a second electrode side in a direction in which the droplet travelsis larger than that on a side opposite to the second electrode.
 4. Thedroplet transport device according to claim 1, further comprising: athird electrode facing the inner wall surface of the through-hole or therecess via the water-repellent film.
 5. The droplet transport deviceaccording to claim 4, wherein an area of a surface of the thirdelectrode parallel to the inner wall surface is larger than an area ofthe first electrode along the surface of the substrate.
 6. The droplettransport device according to claim 1, further comprising: a powersupply that applies a voltage to the first electrode; and a switch thatswitches between an application and a stop of the voltage, wherein thepower supply stops the application after applying the voltage to thefirst electrode for a certain period of time.
 7. The droplet transportdevice according to claim 6, wherein the power supply applies thevoltage to the first electrode until the droplet reaches a ½ position ofa distance between a center of the second electrode adjacent to thefirst electrode and a center of an upper end of the through-hole or therecess.
 8. An analysis system comprising: the droplet transport deviceaccording to claim 1; and an analysis device that analyzes the dropletintroduced into the through-hole or the recess.
 9. The analysis systemaccording to claim 8, wherein the analysis device includes a capillarythat can be inserted into the through-hole or the recess.
 10. Theanalysis system according to claim 9, wherein the analysis devicefurther includes a power supply for applying a voltage to both ends ofthe capillary, and a switch for switching between an application and astop of the voltage by the power supply.
 11. An analysis methodcomprising: preparing the droplet transport device according to claim 1;introducing the droplet onto the substrate; applying a voltage to thesecond electrode to transport the droplet to the first electrode; andapplying a voltage to the first electrode to introduce the droplet intothe through-hole or the recess.
 12. The analysis method according toclaim 11, further comprising: arranging an analysis device at a positionwhere the droplet can be supplied from the through-hole or the recess;and performing analysis on the droplet by the analysis device.